Peter Hartman wrote:I am just curious about what you like or don't like about this design.
Here is the video:
I know it's been ages since you asked this, and it looks like Ernie missed it.
I personally like that Geoff Lawton
design very much.
This design is one of the few I can imagine could be built by relatively handy permies with manageable risks, and the sort of 'on-demand' hot water
that most people
look for when they wax nostalgic about civilized comforts. It's not a "no-brainer" either for design, building, operation, or maintenance, but it handles some tricky problems in simple and clever ways.
I really like Geoff's presentation of it, too; he's a very good teacher.
He does gloss over some of the details.
- how to install waterproof, heat-resistant fittings onto a drum (this is a known art
, but not necessarily a common skill that everyone has);
- galvanic corrosion and proper materials for compatible tank, coils, etc.
- what sorts of supports are needed to keep these layers of material in place; a water
tank is heavy, and there's also thermal expansion tolerance needed.
- insulation needed for firebox and outer shell, to concentrate the heat under the tank. "Standard fireproof insulation" which he mentions is important for efficiency, but that will vary a bit in different regions. Roxul or rock wool
might be good; fiberglass might be OK but might melt; ceramic-fiber would be good but expensive; vermiculite or perlite might work if you could contain it effectively and top up after settling.
- what length of flame path prevents creosote buildup on the tank, or how you clean it once creosote does build up.
- chimney design if building under a shelter
or inside a house
- exactly how you top up, and how you know when it's needed
- how to size and arrange outlets, safety valves, etc. to avoid steam explosions and damage. He gets across the importance of this point nicely, just not the details.
- the relationship between pressurized and non-pressurized water in this system;
- system tolerances for water quality (filtered, alkalinity vs acid, etc), and any risks if water is contaminated or capable of clogging system.
- risks of maintaining a tank of water at warm temperatures over time.
This design brilliantly separates the clean, on-demand hot water
in the coil from any gunge building up in the tank, and the tank protects that on-demand water from overheating while getting it to temperature quickly. He does mention the need to keep the tank topped up; this is a critical safety feature as well as functional consideration. If the coil is clean and only used for potable water, could potentially be used as a potable hot-water generator e.g. make a tea-tap on the side as well as sending it off to the showers.
Points of difference:
I do agree that sticks are easier to burn fast and clean; but I recognize that not everyone is on the small-fuels bandwagon yet.
We routinely use modest cordwood or moderate-sized logs in our rocket heater.
A taller firebox is needed to burn larger fuels cleanly, since any unburned fuels / remaining flames that contact that water tank will deposit creosote.
I love burning stick fuels for sustainability
reasons as well as clean fire, plus they're easier and safer to harvest than timber. Dry faster too. Lumber scrap from projects also works, it doesn't have to be branches or pine cones.
Very dry fuel is as critical for clean fire, or more so.
The smokeless exhaust is a definite point in favor of this heater. I think
he's in a hot, dry climate in Australia, so specifying small fuels is more of an issue than dry fuels. I'd want a dedicated woodshed nearby, with a raised floor to keep fuels above that steam drainage.
My understanding is that later, some people came along and plastered the whole thing in so it looks like a giant water-tower. At least I think that's the same system. Kinda fun to look at, but very hard to get at for maintenance, repairs, or remodels. With big home-built appliances like this, a 'steam-punk' aesthetic where you can see all the working parts is a plus for maintenance and early warning of repairs. Rather than encasing it in plaster or marble, I'd love to see one with stainless steel, or copper and brass detailing, exposed like a samovar.
Indoor construction option:
I would give this clever beast its own stall out back of an outdoor shower
. I'd want more attention to safeties, chimney design, and excellent floor drains before I'd want it in a house with me.
He mentions the need to keep the tank topped up, but the method isn't shown - just a valve. Perhaps that valve is part of the pressurized system and that's why it spits out a lot of steam while it's open.
There's no discussion of 'gunge' buildup (mineral scale, biota growing if the tank is left lukewarm too long, etc) or how to remove it.
The black soot and gunk in the smoke chamber will need to be cleaned out periodically, though perhaps not for several years.
I would hope that at one end or the other, there's a large removable end or lid. I think being able to pull a bung off the tank and hose it out with cold water (shocking the scale off the outside of the pipes and hopefully the inside of the coil) would extend the maintenance life a bit.
Don't know how thick the tank is, whether it's enameled, whether it's a converted commercial tank or a home-built steel drum. A thick or enameled, or stainless, tank inside there would last a lot longer than a repurposed barrel.
If using a barrel, I'd probably leave the paint on except as needed for clean welds; the water inside should
keep the temperature near the boiling point of water, and most industrial drums and water-heater enamels can take those temps and it would offer some protection from corrosion. But a tank upgrade is going to be cheap compared with the added years of use from it; you don't put this kind of system together for a weekend camping trip.
- Exaggeration / time delay of fire - I may have missed a time-lapse flame shot, but he didn't bring a big tank up to boiling on a handful of pine cones.
My guess is the tank's kept warm most of the time by that excellent insulation, and the fire just brought it back up to top heat.
- Steaming hot tap water is lovely if you know how to mix it down, but might not be safe for kids or folks with forgetfulness problems. If you can get an off-grid, thermostatically controlled mixing valve, that does not require electricity (a bimetal valve or something), that would be awesome. A small solar-powered thermostat and mixing valve could also be a nice addition.
It pays to have an experienced hot water tech involved when contemplating such a project
. We heard from a fellow who helped with this system a few years ago, it wasn't just Geoff or generalist students who put it together. I was impressed with his general knowledge and trades experience
; wish I could remember the name, or the details of his background that helped make this system a success on the first prototype.
Relevant experience can come from a range of backgrounds: plumbing, boiler mechanics, steam-fitters, HVAC guys who have worked with radiant floors or steam radiator systems.
Anyone with experience doing other off-grid plumbing projects like solar
hot water will have a definite leg up on the problem solving, supplies, tools, and techniques. Making a couple regular rocket cookstoves or mass heaters
before you try the combo system would be nice
There are just so many little details to manage, like how to protect pipes from freezing, scale, and fire; and of course pressure relief and drainage. Getting the right insulation, and sealing up the things that need to be sealed with good technique and materials, are all going to make things work better.
Here's one of the few threads where Ernie responded to some hot water questions directly: rocket-stove-water-heater thread
. I think I like this design of Geoff's better than the one Ernie describes in the other thread
, in general... but Ernie's would be easier to integrate into our standard rocket mass heater
without altering the firebox or adding supports for the tall weight of a tank.